This invention relates to thermometers and it is particularly concerned with improvements in hot spot thermometers.
While a hot spot thermometer may have other applications, it is especially suited for use in sensing temperature changes in a fluid cooled electric transformer.
A hot spot thermometer is so named because of its structural characteristics whereby it is enabled to be located for temperature monitoring purposes at the spot of hottest temperature development in a transformer. This spot is between the coils of the transformer winding.
This type of thermometer has various advantages. Because it is applied to the hottest area of the transformer, it obtains not only a more accurate reading but also a more rapid indication of temperature changes than would otherwise be provided.
A hot spot theremometer is known from U.S. Pat. No. 3,960,017. It utilizes a high heat resistant ceramic body insertable between the coils of a transformer winding and containing a heat sensitive dielectric rod adapted to vary passage of light through fibre optic elements to produce in an external read-out instrument electrical signals indicative of temperature changes developing in the transformer.
An object of the present invention is to provide a hot spot thermometer which utilizes a high heat resistant ceramic body insertable between the coils of a transformer winding and containing a heat sensitive element which is cooperable with a bellows connected tubing containing a fluid oscillating in the tubing accordingly as the bellows are acted upon by a rocker arm to vary the pressure in the tubing in response to a predetermined temperature sensed.
In accordance with the invention, there is provided the combination comprising an electrical transformer apparatus having a tank containing cooling oil in which the coils of a transformer winding are immersed; and a hot spot thermometer unit having a ceramic body inserted into a space between the coils, a bellows connected to each of the ends of the tubing adapted to cause the fluid to oscillate about the tubing accordingly as one or the other of the bellows is actuated, a rocker arm cooperable with the bellows to alternately actuate one and then the other of the bellows, a loop formation in the tubing disposed in a recess in the body, a heat sensitive element arranged in the recess having a tapered end abutting the loop, the heat sensitive element adapted upon sensing a predetermined rise in temperature to expand its tapered end into squeezing, constricting relation with the tubing and causing as a consequence a rise in the pressure of the fluid as it is the tubing and a corresponding loading of the rocker arm.